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ANNALS OF FAMILY MEDICINE ✦ WWW.ANNFAMMED.ORG ✦ VOL. 11, NO. 2 ✦ MARCH/APRIL 2013

116

ANNALS OF FAMILY MEDICINE ✦ WWW.ANNFAMMED.ORG ✦ VOL. 11, NO. 2 ✦ MARCH/APRIL 2013

116

Screening For Hypertension Annually Compared With Current Practice

ABSTRACTPURPOSE Hypertension is the most common diagnosis in ambulatory care, yet little evidence exists regarding recommended screening intervals or the sensitiv-ity and specifi city of a routine offi ce-based blood pressure measurement, the most common screening test. Screening for hypertension is usually performed by measuring blood pressure at every outpatient visit, which often results in tran-siently elevated fi ndings among adults who do not have a diagnosis of hyperten-sion. We hypothesize that a more limited annual screening strategy may increase specifi city while maintaining sensitivity.

METHODS A retrospective case-control study of 372 adults without hypertension and 68 patients with newly diagnosed hypertension was conducted to compare the usual screening practice of checking blood pressure at every visit with a sec-ond strategy that considered only annual blood pressure measurements.

RESULTS Specifi city improved from 70.4% (95% CI, 65.5%-75.0%) for the usual practice to 82.0% (95% CI, 77.7%-85.8%) for the annual screening strategy. No statistically signifi cant difference in sensitivity existed between the 2 methods.

CONCLUSION A limited annual screening strategy for hypertension can improve specifi city without sacrifi cing sensitivity when compared with routine screening at every visit in previously normotensive adults.

Ann Fam Med 2013;11:116-121. doi:10.1370/afm.1467.

INTRODUCTION

Hypertension is the most common diagnosis for which patients

seek ambulatory care in the United States, representing more

than 42 million visits in 2007.1 Yet there is little evidence to rec-

ommend a screening interval2 or to defi ne the sensitivity and specifi city

of the most common screening test, a routine offi ce-based blood pressure

measurement performed by manual sphygmomanometry. There is univer-

sal agreement among major national primary care organizations, including

The Joint National Committee on Prevention, Detection and Treatment of

Hypertension (JNC-7), the United States Preventative Service Task Force

(USPSTF), the American Academy of Family Physicians, and the Ameri-

can College of Physicians on the utility of screening for hypertension.2-4

JNC-7 recommends a 2-year screening interval for normotensive individu-

als (systolic blood pressure less than 120 mm Hg and diastolic blood pres-

sure less than 80 mm Hg) and a 1-year interval for individuals with prehy-

pertension (systolic blood pressure of 120-139 mm Hg or diastolic blood

pressure of 80-89 mm Hg), but it does not cite any references for these

recommendations.3 The USPSTF mentions the JNC-7 recommendations

regarding screening intervals but states, “the optimal interval for screening

adults for hypertension is not known.”2

Throughout the country, many primary care clinics routinely screen

for hypertension by checking blood pressures at every clinic encounter

regardless of the patient’s chief complaint, previous blood pressures, or

Gregory M. Garrison, MD, MS

Sara Oberhelman, MD

Department of Family Medicine, Mayo

Clinic, Rochester, Minnesota

Confl icts of interest: authors report none.

CORRESPONDING AUTHOR

Gregory M. Garrison, MD, MS

Department of Family Medicine

Mayo Clinic

200 First St SW

Rochester, MN 55905

[email protected]

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117

HYPERTENSION SCREENING

the interval since the last blood pressure was obtained.

Even so, an estimated 30% of individuals with hyper-

tension are unaware they have the disease.3 According

to JNC-7, a diagnosis of hypertension requires “the

average of 2 or more properly measured, seated, blood

pressure readings on each of 2 or more offi ce visits.”3

It is well known that clinic blood pressures tend to be

higher than ambulatory blood pressures, the so-called

white coat effect.5-8 In addition, clinic blood pressures

are often not taken according to JNC-7 specifi cations,

leading to inaccurate and often elevated results.9,10

These factors, plus patient factors of acute pain, illness,

or anxiety, make interpreting clinic blood pressure val-

ues as a screening test for hypertension diffi cult.

With Americans making an average 3.2 medical

offi ce visits per year and the majority of these occur-

ring in primary care,1,12 there is ample opportunity to

design a better, more limited screening strategy for

hypertension that meets JNC-7’s recommendations.3

This pilot study compares the current clinical prac-

tice of screening for hypertension by checking every

patient’s blood pressure at every visit vs a more limited

strategy that screens for hypertension annually.

METHODSWe compared 2 screening strategies for low-risk

patients. The fi rst strategy is the usual clinical practice

of measuring a patient’s blood pressure at every visit.

Because we hypothesized that a limited annual screen-

ing strategy would increase specifi city while main-

taining sensitivity, we simulated a second strategy by

considering blood pressures obtained only at general

medical examination visits and any other visit when it

had been more than 1 year since the last blood pres-

sure measurement was obtained (Figure 1).

To compare the screening strategies, we conducted

a retrospective study for the 5 years preceding August

1, 2010. Subjects were family medicine patients at

Mayo Clinic Rochester who were aged 18 to 75 years

at the start of the study period, were not pregnant,

remained active patients for the entire 5 years, and

had at least 1 offi ce blood pressure recorded during

the study period. We excluded patients with type 1

or 2 diabetes, coronary artery disease, or stage 3 or 4

chronic kidney disease because of the differing stan-

dards for treatment of blood pressure in these indi-

viduals. Additionally, because of the effect on blood

pressure, we excluded patients taking any antihyper-

tensive medications for migraine prophylaxis, periph-

eral edema, or other reasons at any point during the

study period before a diagnosis of hypertension. All

patients had signed a research authorization allowing

retrospective review of their electronic medical record.

The study was reviewed and approved by our Institu-

tional Review Board.

We used an administrative database containing

International Classifi cation of Disease (ICD-9) billing codes

for the past 16 years to construct pools of patients with

hypertension diagnosed during the study period and

patients who did not have hypertension based on the

inclusion and exclusion criteria defi ned previously. We

looked for patients never having an ICD-9 code 401.x

(hypertension) before the start of the study and who

were subsequently given an ICD-9 code 401.x during

the study period, as well as patients who never had an

ICD-9 code 401.x.

We randomly selected 236 patients who received a

diagnosis of hypertension during the study period and

500 normotensive patients using the SAS procedure

survey select (SAS 9.2 , SAS Institute Inc). We screened

for antihypertensive medication use with a computer-

ized text-matching algorithm, and the investigators

conducted a manual chart review of all patients.

We entered data from all study patients regarding

blood pressure values at various outpatient visits, medi-

cations, and demographics into a relational database

(PostgreSQL 8.3, PostSQL Global Development Group,

running on Mac OS 10.7.3). The great majority of blood

pressure measurements were obtained by a licensed

practical nurse using a calibrated aneroid device.

Statistical analysis was carried out using R 2.15.0

statistical software (http://cran.r-project.org/src/base/R-

2/R-2.15.0.tar.gz ) running on Mac OS 10.7.3. Patients

with diagnosed hypertension and patients in the group

Figure 1. Proposed limited annual screening algorithm for hypertension.

BP = blood pressure; CAD = coronary artery disease; CKD = chronic kidney disease; DM = diabetes mellitus; HTN = hypertension.

Low-Risk Patient

Age >18 y; no DM, CAD, CKD, HTN; not pregnant; not on anti-

hypertensive medication

Health maintenance visit?

Last BP >1 y Ago

Record screening BPNo BP screening necessary

No Yes

No Yes

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HYPERTENSION SCREENING

with no hypertension were compared using Fisher’s

exact test for categorical data and t tests for numeri-

cal data. P values of less than .05 were considered

signifi cant. Sensitivity and specifi city, including 95%

confi dence intervals, were calculated for each screening

strategy using the patient as the unit of analysis. Any

blood pressure of 140 mm Hg systolic or 90 mm Hg

diastolic or greater was considered a positive screen-

ing test. A physician’s diagnosis of hypertension was

considered the reference standard for positive disease.

Assuming a sensitivity of 95% and a specifi city of 75%,

with desired 95% confi dence intervals of 5%, it was

estimated 73 patients with diagnosed hypertension and

288 patients without hypertension would be needed.

RESULTSAs is typical for administrative or billing databases,13,14

there were substantial differences from the actual

clinical notes among the 236 potential patients with

hypertension diagnosed during

the study period and the 500

potential patients without hyper-

tension. For instance, 43 patients

in the hypertension group had a

diagnosis of elevated blood pres-

sure without hypertension that

was mistakenly coded as ICD-9

code 401.x; 34 patients never had

a diagnosis of hypertension but

mistakenly were given an ICD-9

401.x billing code, often during a

procedure or hospitalization; and

12 patients in the hypertension

group and 4 patients in the group

with no hypertension were found

to have a clinical diagnosis of

hypertension before the start of

the study that was not recorded

as a ICD-9 401.x billing code in

the administrative database (Fig-

ure 2).

After elimination of the mis-

coded patients, we analyzed data

from 68 patients with hyperten-

sion diagnosed during the 5-year

study period and 372 patients

with no hypertension during the

same period. These 440 patients

had 4,287 blood pressures

recorded. Sex and smoking sta-

tus did not differ between those

with hypertension and those with

no hypertension. The number

of visits per patient per year was also similar, with the

patients with hypertension averaging 2.5 (SD = 2.8)

visits per year and the patients with no hyperten-

sion averaging 1.9 (SD = 1.3) visits per year (P = .096).

Patients with hypertension were older than patients

with no hypertension (47.6 years, SD = 10.4 years

vs 41.2 years, SD = 12.7 years, respectively; P <.001)

and heavier (body mass index 33.6 kg/m2, SD = 6.8 vs

28.6 kg/m2, SD = 8.7 kg/m2, respectively; P <.001). As

expected, average blood pressures were higher in the

patients with hypertension than the patients with no

hypertension. Table 1 summarizes these results.

The screening strategy of checking blood pressures

at every visit identifi ed all 68 patients with hypertension

diagnosed during the study period who had at least 1

positive screening blood pressure higher than 140/90

mm Hg, consistent with the criteria for diagnosis. There

were, however, 110 (29.6%) patients in the group with

no hypertension who were found to have at least 1

blood pressure measurement higher than 140/90 mm Hg

Figure 2. Case and control selection.

BP = blood pressure; CAD = coronary artery disease; CKD = chronic kidney disease; DM = diabetes mellitus; HTN = hypertension.

Patients With Diagnosed

Hypertension

Patients With No

Hypertension

Antihypertensive medication

Manual Chart Review

77 32

43

412

34

2 92

68 372

Elevated BP without HTN

No HTN

Exclusion criteria met

Age >18

CAD/DM/CKD

Pregnancy

No BPs recorded

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HYPERTENSION SCREENING

during the study period. In fact,

266 of 3,299 (8.1%, 95% CI, 7.2%-

9.0%) blood pressures obtained in

this group were at or higher than

140/90 mm Hg. Usual practice, as

expected, had identifi ed 100% of

patients with diagnosed hyperten-

sion (sensitivity 100%, 95% CI,

92.2%-100%), with a specifi city of

70.4% (95% CI, 65.5%-75.0%).

The annual screening strategy

retained 39.3% (1,686) of the

4,287 blood pressures obtained

during the study period. This

method found the same rate of

elevated blood pressures among

the retained readings from

patients with no hypertension,

with 106 of 1,373 (7.7%, 95%

CI, 6.4%-9.3%; P = .692) with

blood pressures at or higher than

140/90 mm Hg. Screening less

frequently resulted in only 67

patients in the group (18.0%)

with no hypertension having

elevated blood pressures. The

annual screening strategy failed,

however, to identify 5 (7.4%)

patients with hypertension on or

before the date of their original

diagnosis. This method yielded

a sensitivity of 92.6% (95% CI,

83.7%-97.6%) and a specifi city of

82.0% (95% CI, 77.7%-85.8%).

Table 2 contrasts the results

obtained by both methods.

DISCUSSIONHypertension screening is an

important part of preventive

health care delivered by primary

care physicians. It is essential to

understand the implications of a screening test’s char-

acteristics to interpret results and design a screening

strategy effectively. This initial pilot study proposes an

annual screening strategy for hypertension using the

most common screening test, the offi ce-based manual

blood pressure measurement, which improves specifi c-

ity while maintaining sensitivity.

SensitivityAn objective of any screening strategy is to classify cor-

rectly those individuals with hypertension. Sensitivity

describes a test’s ability to classify correctly those with

disease (Table 3). With a highly sensitive test, the false-

negative or type 2 error rate is negligible. Thus, a nega-

tive result tends to rule out the possibility of disease.15

As expected, the baseline practice of checking

blood pressure at every visit yielded 100% sensitiv-

ity. The proposed annual screening strategy failed to

identify 7.4% of newly hypertensive patients as quickly

as the baseline strategy. This difference was not signifi -

cant, as the 95% confi dence intervals overlapped. Given

the slowly progressive nature of morbidity resulting

Table 1. Demographic Information on Patients With Diagnosed Hypertension and Patients With No Hypertension

CharacteristicHypertension

(n = 68)No Hypertension

(n = 372) P Value

Sex, No. (%) >.999Male 33 (48.5) 179 (48.1)Female 35 (51.5) 193 (51.9)

Age, year (SD) 47.6 (10.4) 41.2 (12.7) <.001

BMI, kg/m2 (SD) 33.6 (6.8) 28.6 (8.7) <.001

Smoking status, No. (%) .530

Never 28 (66.7) 83 (58.9)

Quit 11 (26.2) 40 (28.3)

Current 3 (7.1) 18 (12.8)

Visits per year, No. (SD) 2.5 (2.8) 1.9 (1.3) .096

Average blood pressure

Systolic, mm Hg (SD) 135.3 (11.1) 114.7 (11.4) <.001

Diastolic, mm Hg (SD) 82.7 (6.7) 70.1 (7.5) <.001

BMI = body mass index.

Table 3. A 2 x 2 Table for Screening Tests for Hypertension

Elevated Screening Blood Pressure Yes No

Yes True positive False positive (type I error)

No False negative (type II error) True negative

SensitivitySn =

TP

TP + FNSp =

TN

TN + FP

Table 2. Sensitivity and Specifi city of Blood Pressure Screening Strategies

Strategy

Hypertension Sensitivity, % (95% CI)

Specifi city, % (95% CI)Yes (Cases) No (Controls)

Typical practice (all visits)

Positive 68 110 100 (92.2-100)

70.4 (65.5-75.0)

Negative 0 262

Limited strategy (annual screening)Positive 63 67 92.6

(83.7-97.6)82.0

(77.7-85.8)Negative 5 305

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from hypertension,16 whether this delay in diagnosis is

clinically relevant is debatable. In this study, we could

not consider visits that occurred after a diagnosis of

hypertension was made, as treatment would affect

these blood pressure values. Thus it was impossible to

ascertain whether and when these patients would have

had hypertension diagnosed using the proposed annual

screening strategy. Considering that hypertensive

patients had an average of 2.5 visits per year, the delay

is unlikely to be more than a few months.

Specifi citySpecifi city describes a test’s ability to correctly classify

those without disease (Table 3). With a highly specifi c

test the false-positive or type I error rate is minimal.

A positive result therefore rules in a disease.15 If large

numbers of disease-free individuals are screened

repeatedly, then even highly specifi c tests can generate

unwieldy numbers of false-positive results, for which

patients must undergo further testing.

This study found that the baseline practice of

screening for hypertension by checking blood pres-

sures at every offi ce visit has a poor sensitivity of

70.4%. During the 5-year study period, 29.6% of

adults who never had hypertension diagnosed had at

least 1 elevated blood pressure reading. These ele-

vated readings can lead to follow-up visits, laboratory

testing, and patient anxiety, or as in “The Shepherd’s

Boy and the Wolf,”11 they can lull the physician into a

sense of complacency, delaying the diagnosis of actual

hypertension.

One way to compensate for a screening test’s poor

specifi city is to target a limited population for screen-

ing; however, JNC-7 recommendations clearly indicate

the need to screen all adults for hypertension.3

In slowly progressive diseases, another way to

compensate for poor specifi city is to reduce the fre-

quency of screening.17 Obviously, clinical consider-

ations come into play as the screening needs to occur

frequently enough to detect the disease in its earliest

stages, when it is easily treated and before morbidity

develops. Mild to moderate hypertension is a slowly

progressive chronic disease that causes complications

and target organ damage over the course of years.16

Given a test with high sensitivity but poor specifi city,

such as offi ce blood pressure screening, performing it

too frequently increases false-positive results but does

not improve disease detection.

Less frequent screening is the tactic applied by

our proposed annual screening strategy. It reduced

the number of screenings performed by 60.7%. The

reduced frequency of screening produced a signifi cant

decrease in the false-positive rate from 29.6% to 18.0%

of nonhypertensive adult patients over a 5-year period.

Applied to the roughly 2,000 healthy adults cared for

by a typical family physician, it results in 232 fewer

patients needing further workup over 5 years.

Reducing the number of unnecessary blood pres-

sures screenings in healthy adults provides benefi ts

in addition to improving the false-positive rate. It can

increase clinic effi ciency, reduce clerical burdens, and

focus attention on accurately obtaining screening

blood pressure measurements. JNC-7 specifi es that an

accurate blood pressure measurement should be the

mean of 2 auscultatory readings taken with an appro-

priately sized cuff with the patients’ feet on the fl oor

and arm supported at heart height after being seated

quietly in a chair for 5 minutes.3 In the typical busy

family medicine clinic with 15-minute appointments,

there is no time for this method for every patient at

every visit.6,18 Instead, patients are all too often rushed

down the hallway from a waiting room, and a blood

pressure is immediately measured. Reducing the fre-

quency of screening blood pressures may allow clinical

staff time to measure blood pressures more accurately.

For instance, oscillometric devices, such as the BpTRU

(BpTRU Medical Devices), that take multiple readings

over several minutes may be used.19

LimitationsIdentifying patients with newly diagnosed hyperten-

sion by ICD-9 codes proved problematic. Manual chart

review revealed substantial inaccuracies leading to

fewer patients than originally forecast, which limited

the study’s ability to detect differences in sensitivity

between the 2 methods. The fewer patients did not

affect the study’s primary aim of detecting differences

in specifi city, however.

Determining a group of patients with no hyperten-

sion was also problematic. This study used a 5-year

time frame to look for the development of hyperten-

sion, and thus we do not know what happens in the

future to patients who did not have hypertension

diagnosed but who had elevated blood pressures. Do

they go on later in life to develop hypertension? Addi-

tionally, we did not design our study to examine the

effect that our proposed screening strategy might have

on morbidity from hypertension. Further studies with

longer time frames and other endpoints are required to

answer these questions.

The proposed annual screening for hypertension (in

line with selection criteria for blood pressure measure-

ments in this analysis) would entail measuring blood

pressure for each patient at all preventive care visits or

if it had been at least 1 year since the last blood pres-

sure measurement. This simplistic approach makes the

algorithm easy to understand and implement, but it

may overlook other important clinical factors.

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Age and body mass index are well-established risk

factors for hypertension,20,21 and the observed differ-

ences between patients with diagnosed hypertension

and patients with no hypertension are not surprising.

Such differences did not affect our sensitivity and

specifi city analysis.

The choice of a physician diagnosis of hypertension

as the reference standard for disease may underestimate

its prevalence in the study population.3 JNC-7 provides

a defi nition for hypertension as “the average of 2 or

more properly measured, seated blood pressure read-

ings on each of 2 or more offi ce visits.”3 Unfortunately,

very few routinely obtained, offi ce-based blood pressure

measurements meet the requirements of this defi ni-

tion.9,10 Thus using the JNC-7 defi nition as the reference

standard for hypertension in this study was impracti-

cal, as there was no guarantee that the retrospectively

obtained blood pressures met the rigorous requirements.

Although a limitation, it is not necessarily a weakness,

because the purpose of this study was to investigate the

screening utility of routinely obtained typical offi ce-

based blood pressure measurements, which do not

always meet the strict JNC-7 requirements.

Finally, there is a distinction between obtaining a

blood pressure reading for hypertension screening pur-

poses and obtaining a blood pressure reading because it

is clinically relevant. There are many clinical scenarios,

such as chest pain, palpitations, lightheadedness, and

severe infections, where obtaining a blood pressure mea-

surement is necessary to guide diagnosis and treatment

decisions, but the purpose is not to screen for hyperten-

sion. This study does not suggest that these blood pres-

sures should not be obtained; only that they should be

interpreted cautiously when diagnosing hypertension.

To read or post commentaries in response to this article, see it online at http://www.annfammed.org/content/11/2/116.

Submitted March 13, 2012; submitted, revised, July 28, 2012; accepted August 21, 2012.

Key words: hypertension; blood pressure; blood pressure determi-nation; preventive health services; sensitivity and specifi city; mass screening

Funding support: Funding was provided by Mayo Clinic Department of Family Medicine.

Acknowledgments: We would like to thank Melissa Gregg and Julie Maxson for their assistance with data collection. Without their expertise, this study would not have been possible.

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